In general, an internal combustion engine having a valve mechanism of an overhead cam shaft type such as for example an automotive vehicle engine is required to transmit the rotation of a crankshaft disposed at the lower portion of the engine to a camshaft disposed at the upper portion of the engine. In order to normally operate the valve mechanism, the rotation of the crankshaft is required to be synchronized with the rotation of the camshaft. For this purpose, there have so far been used various kinds of timing belts as transmission means for transmitting the rotation of the crankshaft to the camshaft.
The timing belt thus used can function to synchronize the rotation of the crankshaft with the rotation of the camshaft. However, there is a possibility that the timing belt cannot synchronize the rotation of the crankshaft with the rotation of the camshaft when the timing belt is unexpectedly damaged.
For this reason, there have so far been proposed a wide variety of power transmission apparatuses one of which is constructed to inform a driver of a belt exchanging time to exchange a deteriorated timing belt with a new timing belt shortly before the timing belt is damaged. One of known power transmission apparatuses is constructed to calculate a fatigue level of an annular power transmission member such as the timing belt on the basis of the rotational speed and the operation time of the engine to issue such a warning that the timing belt is required to be exchanged when the fatigue level exceeds a predetermined threshold value (for example see Patent Document 1).
The power transmission apparatus previously mentioned can appropriately judge whether the timing belt reaches or does not reach the belt exchanging time of the timing belt as compared with the conventional power transmission apparatus constructed to judge the belt exchanging time of the timing belt only based on the travel distance of the vehicle.